On 8/14/23 20:18, John Dammeyer wrote:
Hi Gene,
It's why I'm filtering. And yes. I agree, at this slow a speed I suspect
what I will find is two different velocities reported from edge to edge.
I'm guessing when the speed is fast (small gap) then a faster than required
distance/vel is implemented. Then on the next wider pulse it's gone too
far and now the drive stops because it has overshot.
I'm guessing.
I'll let you know.
John
This is something that halscope, watching the encoder output, could also
tell you. If while looking at it. you see a 4 step pattern that
essentially repeats itself, that encoder is duff. First, it needs lots
higher definition. 240 edges per turn needs a lot higher precision than
a 1000 line=4000 edges per turn, spinning at 7 or 14 times the spindle
rpms gives 100's of times smoother control. That $20 Omron now has 9
years of spinning at up to nearly 21,000 revs, rated at 6000 and hasn't
sneezed yet.
You aren't going to get smooth z motion until you've got smooth, silent
spindle motion. Its following what it thinks is the spindle speed as
output from the encoder If the encoder is outputting noise, z is going
to try and follow it.
Good luck John.
-----Original Message-----
From: gene heskett [mailto:ghesk...@shentel.net]
Sent: August 14, 2023 1:31 PM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] Rigid tapping
On 8/14/23 15:53, John Dammeyer wrote:
This thread has some good information about this
https://sourceforge.net/p/emc/mailman/message/34363029/
For interest sake I set my mill up to turn 1 RPS with my 60 tooth
non-symmetrical encoder (4mm slots, 2.5mm teeth) and then ran the
power
tapping G-Code to see what the knee Z axis would do.
What I found is that it moved in short spurts. Putting my finger on the
knee and against the column it still appeared to move rather slowly with
less of a jerk. All this makes sense of course.
Something might be off in the quadrature accuracy. Do you have a dual
trace triggered scope? That will likely be quite helpful. 60 teeth,
non-symetrical is going to generate a horrific amount of quantization
noise because neither waveform is going to be a 50/50 ratio in the time
domain. I got rid of all signs of that by putting my $20 Omron encoder
encoder on the rear of the spindle MOTOR, making and index pulse
generator on the spindle with a glued on screw and an ATS-667 hall
device, and tally switches on the heads gearshift knob to electronically
change gears. So the SCALE changes with the gearshift knob. And I can
run the pid's Pgain above 20.
My servo period is 1000000 nanoseconds or 1 ms. At 1 RPM that's one
tooth
every second or 4 encoder edges per second meaning one edge every
250mS.
That's 250 servo periods. What I think I'm seeing is that every 250
servo
periods the system detects the encoder edge and knows it's moved
1/240th of
the 20 TPI thread. (0.000208333") So it tells the Z axis to move that
same
distance and I suspect the velocity setting of 0.0002083333/250mS.
Does that make sense? Is there a way to log each Z axis speed/distance
command so I can see what it's doing?
Or have I misunderstood how the power tapping synchronized motion is
done.
Thanks
John
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Cheers, Gene Heskett.
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_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
.
Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
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